1. Field of the Invention
This invention relates to a liquid crystal panel unit and also to a liquid crystal projector using such a panel unit. More particularly, the present invention relates to a panel unit applicable to a reflection type LCD panel to be used in the image display section of a projection type image display apparatus such as a linear projection display for audiovisual (AV) applications or a data projector for displaying computer outputs.
2. Related Background Art
FIG. 3 of the accompanying drawings schematically illustrates a known image display apparatus (LCD panel unit) comprising an LCD panel and a substrate for holding the LCD panel (hereinafter referred as holding substrate).
Referring to FIG. 3, the LCD panel 5 is typically constituted by a liquid crystal drive substrate (active matrix substrate) 1 formed by arranging pixel electrodes into a matrix on a semiconductor substrate, an opposite substrate 2 having a transparent electrode and a liquid crystal layer 4 held between the liquid crystal drive substrate 1 and the opposite substrate 2 and securely bonded to said holding substrate 10 by way of an adhesive layer 8.
With the above arrangement, the image displaying surface of the LCD panel 5 can show a varying height within the effective image area of the LCD panel 5 as observed from the rear surface of the holding substrate 10 due to the varying thickness of the adhesive layer 8 held between the LCD panel 5 and the holding substrate 10.
The image projected for viewing by a projection display comprising such an LCD panel unit is in fact an image obtained by magnifying the one produced on the LCD panel 5 by means of the projection lens of the projection display. The sharpness of such an enlarged and projected image is determined, if partly, by the focal point of the image that has to be located on the screen. In other words, the sharpness of the image displayed by the projection display depends on if the image displaying surface of the LCD panel 5 is found within the depth of field of the projection lens or not.
Currently, there is a strong trend of down-sizing the LCD panel by densely arranging dimensionally reduced pixels on the LCD panel in order to meet the demand for high definition images to be realized by down-sized display apparatus. Additionally, to survive the highly competitive scene for the technological development of projection displays, the magnification of the projection lens has to be raised to produce a remarkably enlarged projected image. However, the depth of field of the projection lens is inevitably reduced if the plane of projection is held invariable while the magnification of the projected image is increased. Then, the LCD panel has to be accurately and securely held to the local point of the projection lens. A projection lens with a magnification of fifty times will be required to project an image from a 1-inch LCD panel onto a 50-inch screen, although the magnification may vary depending on the distance of projection and the performance of the lens. Thus, if a projection lens with a magnification of the order of tens is used to produce a bright image, the depth of field of the projection lens will be as small as tens of several microns.
However, as pointed out above, known LCD panels has an image displaying surface that can show a height that varies by tens to hundreds of microns as observed from the rear surface of the holding substrate.
Then, if the distance between the holding substrate and the projection lens is accurate, the projected image can become blurred, although partly.
Meanwhile, a projection display comprising an LCD panel is required to produce a highly bright projected image. Then, light from the light source has to be made to strike the LCD panel with an enhanced intensity. The intensity of light striking the LCD panel is also raised as the LCD panel is dimensionally reduced. As a result, the temperature of the LCD panel will inevitably be raised in operation. In the case of a known LCD panel having a 1.3-inch diagonal and provided with a 250 W metal halide lamp, the temperature of the LCD panel rises to about 40xc2x0 C. when a thermally not-highly-conductive adhesive agent is used for the adhesive layer of the LCD panel. If the adhesive agent is made to contain a heat-emitting filler material, the temperature rise shows only a limited improvement and the temperature of the LCD panel is raised to about 35xc2x0 C. in operation.
Therefore, the effect of the adhesive layer arranged between the holding substrate and the LCD panel for emitting heat from the LCD panel to the holding substrate is currently not satisfactory and the temperature rise entails problems including a degraded image quality.
Japanese Patent Application Laid-Open Nos. 55-65928, 7-84267 and 8-211351 disclose the use of spacers between the paired substrates carrying thereon a liquid crystal layer in order to realize a uniform thickness for the liquid crystal layer. However, the above listed patent documents do not refer to any of the above identified problems.
In view of the above described circumstances, it is therefore an object of the present invention to provide an LCD panel of the above identified type having an image displaying surface that shows a uniform height as observed from the rear surface of holding substrate.
Another object of the present invention is to provide an LCD panel that can effectively reduce its temperature by emitting heat to the holding substrate in operation.
According to the invention, the above objects and other objects of the invention are achieved by providing a liquid crystal panel unit comprising an LCD panel having a pair of substrates and a liquid crystal layer arranged between said substrates and a holding substrate for holding the LCD panel by rigidly securing one of said substrates thereto, characterized in that a plurality of protuberances are formed on the surface of said holding substrate at a side thereof and said one of the substrates is rigidly secured to said holding substrate with the side carrying said protuberances facing inside.
According to the invention, the image displaying section of the LCD panel can be made to show a uniform height as observed from the rear surface of the holding substrate by securing the LCD panel to the holding substrate. With the above arrangement, an enhanced degree of sharpness can be ensured for the projected image over the entire plane of display by controlling the distance between the holding substrate and the projection lens.
Additionally, according to the invention, the protuberances of the holding substrate and the LCD panel may be held in tight contact. According to the invention, it may be so arranged that an adhesive layer containing no filler material is pinched between the flat tops of the protuberances and the LCD panel while an adhesive layer containing a filler material is laid to fill the space unoccupied by the protuberances between the holding substrate and the LCD panel. With such an arrangement, heat can be emitted quickly and efficiently to the holding substrate if the temperature of the LCD panel rises.
The adhesive layer containing a filler material and showing an high thermal conductivity that fills the space unoccupied by the protuberances between the holding substrate and the LCD panel can effectively promote the emission of heat from the LCD panel to the holding substrate and lower the temperature of the LCD panel.